Two forms of Energy Transfer • Work (w) – Work = force x distance • Force (newton) = mass x acceleration = kgm/s 2 – Work = (kgm/s 2 )(m) = kgm 2 /s 2 = joule – Work can also be done by a gas with the equation • W = -P V • Heat (q or Q) – transfer of thermal energy between two bodies that are different temperatures – Measured in joules Temperature = Thermal Energy
Energy, Heat, and Work • You can think of energy as a quantity an object can possess or as a collection of objects. • You can think of heat and work as the two different ways that an object can exchange energy with other objects. – Either out of it, or into it
• The amount of kinetic energy an object has is directly proportional to its mass and velocity. KE = ½ mv 2 Units of Energy • When the mass is in kg and velocity is in m/s, the unit for kinetic energy is . • 1 joule of energy is the amount of energy needed to move a 1 kg mass at a speed of 1 m/s.
One joule in everyday life represents approximately: • the energy required to lift a small apple (weighing approximately 100 g) vertically through one meter. • the energy released when that same apple falls one meter to the ground. • the heat required to raise the temperature of 1 g of water by 0.24 K. • the typical energy released as heat by a person at rest, every 1/60th of a second. • the kinetic energy of a 50 kg human moving very slowly (0.2 m/s). • the kinetic energy of a tennis ball moving at 23 km/h (6.4 m/s).
System vs Surroundings • In any thermodynamic study, the first step is to define the system . • System – the actual physical or chemical change taking place – Open system, closed system or isolated system • Surroundings – the rest of the universe outside of the system • In chemistry we usually study the system (the reaction) and most reactions are a closed • What we study is the exchange of energy between the system and the surroundings open closed isolated
8 First law of thermodynamics – energy can be converted from one form to another, but cannot be created or destroyed. Chemical energy lost by combustion = Energy gained by the surroundings system surroundings Can test the 1 st law by measuring only the change in the internal energy of a system between its initial state and its final state in a process. E Change in Internal Energy
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